1. Field of the Invention
The invention relates to a threaded tubular connection comprising a male tubular element comprising a male threading and a female tubular element comprising a female threading which cooperates by makeup with said male threading, the axial width of the threads of said threadings and/or the intervals between said threads varying progressively along the axis of the connection over at least a portion of the axial length of the threadings, such that the threads of each threading are housed with an axial clearance in the intervals of the other threading at the start of makeup, said clearance progressively decreasing until it becomes zero during makeup.
2. Discussion of the Background
The term “sealed contact” as used here means contact between two surfaces pressed hard against each other to produce a metal-to-metal seal, in particular a gas-tight seal.
Threaded connections of this type are well known, in particular for use in oil and gas wells. They generally have threads with a dovetail profile as described, for example, in U.S. Re 30 647 and U.S. Re 34 467. They suffer from a number of drawbacks. Firstly, the geometrical characteristics of progressive interfering threads cannot ensure a gas-tight seal. Such a seal is difficult to obtain with abutment surfaces separate from the threadings; sealing surfaces demand very accurate relative positioning of the two elements at the end of makeup. However, the final relative position of the elements is in this case strongly influenced by the machining tolerances for the threads. The use of tapered sealing surfaces with a small taper and thus a small vertex angle, which are more tolerant as regards axial position, does not constitute a satisfactory solution as such bearing surfaces are extremely sensitive to the phenomenon of galling, which result in spoiling after only a few makeup-breakout operations.
A further disadvantage of said known threaded connections is that the geometric characteristics of the threadings do not encourage evacuation of the lubrication grease used for makeup. This grease can accumulate locally, for example between the thread crests and roots, giving rise to very high pressures which in their turn perturb proper positioning of the elements and contact of the sealing surfaces.